1. Field of the Invention
The present invention relates to an automatic dispersion compensating optical transmission for performing an automatic dispersion compensation by a repeater in a long distance, light-based transmission in which an optical signal transmitted from mainly an optical transmitter through a transmission line is directly amplified by the repeater.
2. Description of Related Art
In a long distance, light-based transmission which uses a high dispersion optical fiber as a transmission line, a signal waveform distortion has occurred due to dispersion and a correct waveform transmission has become impossible. Therefore, an application of a dispersion compensation by means of a dispersion compensation device such as a dispersion compensating fiber (referred to as "DCF", hereinafter) has become indispensable. A required amount of dispersion compensation depends upon a distance of transmission and a dispersion characteristics of optical fiber.
An optical communication system disclosed in Japanese Patent Application Laid-open No. H7-202798 is one of examples of the known techniques related to the dispersion compensation in a long distance, light-based transmission. In this optical communication system, a long distance, light-based transmission rate is increased by making a length of the DCF used to dispersion compensation a half of a usual length of the DCF. Further, in an optical wavelength multiplex transmission system and an optical dispersion compensation system disclosed in Japanese Patent Application Laid-open No. H7-107069, a capacity of the optical communication system is increased by applying the dispersion compensation in order to realize the wavelength multiplex transmission.
In general, the amount of dispersion compensation of the DCF has to be set to an optimal value which depends upon a transmission distance thereof as mentioned above. Therefore, when the transmission line is switched to a preliminary line, it is necessary to set the amount of dispersion compensation again to an optimal value of the preliminary line by replacing the DCF. However, it is impossible in the conventional system to automatically switch between DCF'S.
Incidentally, since, in the case of the optical communication system disclosed in the aforementioned Japanese Patent Application Laid-open No. H7-202798, the length of the DCF used to compensate for the dispersion is made a half of the usual length, it can not be adapted to a case where the amount of dispersion of the transmission line is changed. Further, in the case of the dispersion compensation system disclosed in the aforementioned Japanese Patent Application Laid-open No. H7-107069, the dispersion compensation is applied for the wavelength multiplex transmission and it is impossible to control the amount of dispersion compensation correspondingly to the transmission lines.